The fourth generation (4G) mobile communication system, which is the next-generation communication system, has cells of quite small radius to accommodate rapid communications and more traffic. It is anticipated that the centralized design is almost impossible using a current radio network design scheme. In this respect, the 4G communication system needs to be controlled and implemented in a distributed manner and to actively cope with an environmental change such as joining of a new base station. This is why the 4G communication system requires a self-configurable wireless network.
To actually implement the self-configurable wireless network required in the 4G communication system, it is necessary to adopt a technique of an ad-hoc network to the wireless communication system. For example, a multihop relay cellular network adopts a multihop relay scheme of the ad-hoc to the cellular network including a stationary base station.
Transceiving signals through a direct link between the fixed base station and a terminal, a typical cellular communication system can easily configure the radio communication link of high reliability between the base station and the terminal. Yet, the cellular communication system is subject to low flexibility in the wireless network configuration because of the fixed position of the base station. As a result, a cellular communication system scarcely provides effective communication services in a wireless environment under frequent changes of the traffic distribution or the required traffic.
To address those shortcomings, a cellular wireless communication system can employ a multihop relay data delivery scheme using a fixed or mobile relay station or general terminal. A multihop relay wireless communication system is able to reconfigure the network in prompt reaction to a communication environmental change and to operate the entire wireless network more efficiently. For example, the multihop relay wireless communication system can extend a cell service coverage area and increase system capacity. In a poor channel condition between the base station and the terminal, a radio channel of better channel condition can be provided to the terminal by installing a relay station between the base station and the terminal and establishing a multihop relay path via the relay station. Also, in a cell boundary under the hostile channel condition from the base station, the multihop relay scheme can offer the rapid data channel and the extended cell service coverage.
FIG. 1 depicts a general multihop relay cellular network.
A first mobile station (MS1) in a coverage of a base station (BS) is connected to the BS through a direct link. A second mobile station (MS2), which travels outside the coverage of the BS and suffers bad channel condition from the BS, is connected to the BS via a relay station (RS). In the cell boundary of the BS or in a shadow region shielded by buildings, the MS2 communicates with the BS via the RS. As such, in the cell boundary under the hostile channel condition, the multihop relay scheme can provide the rapid data channel and extend the cell service coverage.
A broadband wireless access (BWA) communication system based on Institute of Electrical and Electronics Engineers (IEEE) 802.16 standard performs the ranging using a Code Division Multiple Access (CDMA) code to request the bandwidth. To request the bandwidth, the MS2 selects one ranging code at random among a CDMA code set (or a ranging code set), maps the selected ranging code to a random ranging slot, and then transmits the ranging code to the BS.
When the ranging is applied to the multihop relay system, MS1 directly communicating with the BS can operate the same as before. However, when the MS2 communicates via the RS, the RS needs to relay the ranging code from the MS2 to the BS or inform the BS of the information relating to the received ranging code.
If the RS relays the ranging code over the ranging region allocated to the MS2, the BS cannot tell whether the ranging code is received from the MS2 or the RS because the ranging code does not include terminal information. Hence, the ranging code can be dividing into an MS ranging code and an RS ranging code. In this case, the code discrimination is feasible but the probability of the code collision is likely to rise because of the reduced range (or number) of the substantially available codes. Alternatively, a ranging region dedicated to the RS can be used, which would otherwise disadvantageously cause the resource waste.